Liver regeneration has been studied in necrotic hepatitis of 21 rabbits infected with the haemorrhagic disease virus (VHD). Formalin fixed and paraffin embedded liver sections have been immunostained for the proliferation associated antigen PCNA (Proliferating Cell Nuclear Antigen-clone PC10) and counterstained with toluidine blue that enhances histologic recognition of mitoses. Hepatocyte and bile duct proliferative activity has been quantified, by means of image analysis, both as PCNA reactivity and mitotic activity. The results, compared with a semiquantitative estimation of liver necrosis, showed a positive correlation between hepatocyte proliferative activity and liver necrosis, both in acute and subacute hepatitis. In the chronic phase a residual proliferative activity appeared in bile duct cells.